The functional role of the basal ganglia in achieving controlled movement and postural adjustment and the neural systems by which this control is achieved are poorly understood. Electrophysiological recording of the activity of putamen and pallidal neurons in unanesthetized, behaving monkeys will allow us to address several questions related to these problems: 1. What types and proportion of neurons in putamen and globus pallidus change their firing rate in temporal relationship to postural adjustments made by a monkey whose base of support is tilted? 2. Are the changes particularly correlated to position, velocity, or acceleration phases of the paradigm? 3. How do different sensory inputs (visual, labyrinthine, neck receptor) contribute to any changes in firing pattern? 4. Does the firing pattern of individual basal ganglia neurons change when the same muscle participates in different motor patterns, i.e., reciprocal activation vs. cocontraction? The spinal-destined systems via which basal ganglia output can influence motoneurons will be investigated by implanting stimulating electrodes in the globus pallidus and examining the effects of pallidal stimulation on the activity of motor cortex and reticulospinal neurons.